v21n14

DEPARTMENT OF PATHOLOGY
The Johns Hopkins Medical Institutions

Vol. 21, No. 14
THE JOHNS HOPKINS MICROBIOLOGY NEWSLETTER
Tuesday, April 30, 2002

Provided by Karen Fujii, Division of Outbreak Investigation, Maryland Department of Health and Mental Hygiene.

2 outbreaks were reported to DHMH during MMWR Week 17 (April 21 - April 27):
1 rash illness outbreak at a school in Baltimore City.
1 Shigella outbreak at a daycare in Baltimore County.

The Johns Hopkins Hospital, Department of Pathology, Information provided by, Jeffrey L. Seibel, MD, PhD,

Case description: A 71 year-old female presented to her primary care physician with a poorly healing laceration on the dorsum of her left third digit. Three weeks prior she had been preparing fish when the knife slipped and cut superficially into the hand. She cleaned the wound with soap and water and bandaged it. Over the next three weeks, the hand became swollen and increasingly painful, with intermittent drainage of pus-like material. A two-week course of amoxicillin/clavulanic acid and ciprofloxacin failed to heal the wound, as did a course of clarithromycin. The patient was seen at The Johns Hopkins Hospital. On examination, the patient was afebrile. The dorsum of the hand showed a 2 mm wound covered by a honey-colored scab. Proximal to the wound two fluctuant masses are palpated, roughly 1 cm in diameter each. No fluid was expressed by palpation at that time. A radiograph showed minimal diffuse osteoporosis of the left hand and wrist. The wound was surgically debrided, yielding purulent drainage that was cultured for aerobic and anaerobic bacteria, fungi and mycobacteria. The mycobacterial culture grew Mycobacterium marinum.

Organism: Mycobacterium marinum is distributed worldwide in both salt and fresh water. It is a common inhabitant of swimming pools, aquariums and water-cooling towers. The most common activity associated with infection is cleaning of aquariums. Handling of fish, as in this case, is also common. The organism was first identified in 1926 in saltwater fish, and has also gone by the names M. platypoecilus and M. balnei.

Clinical manifestations: The infection usually causes solitary subcutaneous lesions at the site of trauma, although approximately one-third may show multiple lesions along lymphatic drainage. They lesions are usually small violet papules that may progress to superficial crusty ulcers with scarring. Most lesions remain localized to the skin, however cases of tenosynovitis, bursitis and even osteomyelitis have been reported. In severely immunocompromised patients widely disseminated disease can occur.

Diagnosis: M. marinum stains with standard acid-fast techniques, and appears somewhat elongated and wider than M. tuberculosis. Cross-barring markings may also be seen (not a specific finding). The DNA probes typically tested (M. tuberculosis complex, M. kansasii, M. gordonae, M. avium-intracellulare complex) are negative. An initial clue to the identification is the fact that the organism grows well at 30-32 degrees C, but poorly or not at all at 37 degrees C. Colonies appear within 8-14 days and are yellow-pigmented if grown in the presence of light (photochromogenic, Runyoun group I). Biochemical assays are helpful, such as the failure to reduce nitrates to nitrites, lack of urease activity, hydrolysis of Tween and lack of heat-stable catalase. Analysis of cell wall fatty acids by gas liquid chromatography is also useful.

Treatment: Combination chemotherapy with drugs such as rifampin and ethambutol is standard. Clarithromycin, TMP/sulfa and others may also be effective. The course of therapy is typically between 12 and 24 weeks, and is continued for 4-8 weeks after the lesions disappear clinically. Deep infections often require surgical debridement in addition to chemotherapy.

References:
1. Koneman et al. Color Atlas and Textbook of Diagnostic Microbiology, 5^thEdition, Lippincott-Raven, Philadelphia, 1997

2. Jernigan JA and Farr BM. Incubation period and sources of exposure for cutaneous Mycobacterium marinum infection: Case report and review of the literature. Clin Infect Dis (2000); 31:439-443.

3. Brown BA and Wallace RJ. In, Principles and Practice of Infectious Diseases, 5^th Edition. Edited by GL Mandell, JE Bennett, and R Dolan. Churchill Livingstone, Inc., Philadelphia, 2000.